AT1367A Datasheet, PDF (8/14 Pages) Aimtron Technology – 1MHz, 800mA Synchronous Buck Converter With Power Good Detector & LDO

AT1367A/B/C/D
Preliminary Product Information
1MHz, 800mA Synchronous Buck Converter
With Power Good Detector & LDO
Typical Application Circuits ( Continued )
10nF
27nF
To DSP
To DSP
100K 100K
VBG
VCC
AGND
DELAY
/PG
PG
SW
AT1367B ^PGND
OUT1
OUT2
VIN
5.0V
10uF
4.7uH
0.1uF 1M
10uF
VOUT1
3.3V/300mA
100K
VOUT2
1.8V/400mA
2.2uF
From /PG
Figure 5
Application Information
Capacitor Selection
In continuous mode, the source current of the top MOSFET is square wave of duty
cycle. The Primary function of the input capacitor is to provide a low impedance loop
for the edges of pulsed current drawn by the AT1367A/B/C/D. A load step at the
output can induce ringing at the input VIN. This ringing can couple to the output and
be mistaken as loop instability. The oscillation can be improved by add the
capacitance of the input capacitor. A typical value is 10µF ceramic (X5R or X7R),
POSCAP or Aluminum Polymer. These capacitors will provide good high frequency
bypassing and their low ESR will reduce resistive losses for higher efficiency. The
input capacitor RMS current varies with the input voltage and the output voltage. The
equation for the maximum RMS current in the input capacitor is:
I _RMS = I_OMAX
V_{O (1 −} V_{O )}
V_IN
V_IN
7F, No.9, Park Avenue II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: [phone] Fax: [phone]
WWW: http://www.aimtron.com.tw
3/2/2006 REV:1.2
Email: [e-mail]
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